Ana səhifə

Prepared for

Yüklə 145.5 Kb.
ölçüsü145.5 Kb.
  1   2   3

community structure of fish and macrobeNthos
at selected sites fronting sand island, o‘ahu,
in relation to the sand island deep ocean outfall,
YEAR 3—1992

Richard E. Brock

Special Report 01.29:93

January 1993


City and County of Honolulu

Department of Public Works

Project Completion Report


“The Assessment of the Impact of Ocean Outfalls
on the Marine Environment off O‘ahu, Hawai‘i”

Project No.: C-59390

Project Period: 1 November 1992–31 January 1993

Principal Investigator: Roger S. Fujioka


University of Hawaii at Manoa

Honolulu, Hawaii 96822


This report constitutes the third year of an annual monitoring (carried out on 21–22 December 1992 and 25 January 1993) of shallow marine communities inshore of the Sand Island deep ocean outfall. This quantitative monitoring effort focuses on benthic and fish community structure and is designed to detect changes in these communities. Marine communities offshore of Honolulu have received considerable perturbation over the last 100 years. Raw sewage was dumped in shallow water until 1978; point and non-point sources of pollution from both urban sources and industry continue. All of these disturbances may serve to obscure any possible impacts from the deep ocean outfall discharge. The marine communities show a considerable range in development that is probably related to past (historical) impacts. Stations have been sited to take advantage of these gradients. Analysis of the first year’s data showed that there had been no statistically significant change in the biological measures (i.e., percent coral cover, number of coral species, number of invertebrate species, total number of invertebrates counted, number of fish species, total number of fishes counted, and the biomass of fishes present at each station) quantified in the study during that period. Hurricane Iniki which occurred in September 1992 impacted marine communities along the south shore of O‘ahu. Considerable damage was incurred by the coral communities especially at the westernmost study site. Despite the considerable impact of this storm, statistical analysis of the most recent data show that the changes which have occurred are not statistically significant.



In recent years controversy has arisen regarding the impact that sewage effluent from the Sand Island Wastewater Treatment Plant may have on inshore coral reef species. Much of the geographical area of concern in this study was impacted by the release of 3 m3/sec (62 mgd) of raw sewage in 10 m of water off Sand Island from 1955 to 1977. Starting in 1978 sewage received advanced primary treatment and was released further offshore of Sand Island from a deep ocean outfall (67–73 m depth). Despite studies that demonstrated the recovery of inshore benthic communities once the shallow sewage stress was removed (e.g., Dollar 1979), concern continues over the possible impact that the release of sewage from the deep ocean outfall may be having in the shallow (< 20 m) marine communities fronting Honolulu and Sand Island. Accordingly, this study was undertaken commencing in 1990 in an attempt to quantitatively ascertain the impacts that may be occurring. This document presents the results of the third annual survey carried out in 1992.


Marine environmental surveys are usually performed to evaluate the feasibility of an ecosystem response to specific proposed activities. Appropriate survey methodologies reflect the nature of the proposed action(s). An acute potential impact (as channel dredging) demands a survey designed to determine the route of least harm and the projected rate and degree of ecosystem recovery. Impacts that are more chronic or progressive require different strategies for measurement. Management of chronic stress to a marine ecosystem demands identification of system perturbations which exceed boundaries of natural fluctuations. Thus a thorough understanding of normal ecosystem variability is required in order to separate the impact signal from background “noise.” Infrequent natural events may add considerably to the variability or background “noise” measured in a marine community. In September 1992 Hurricane Iniki struck the Hawaiian Islands and impacted some marine communities along O‘ahu’s south shore. This rare event has provided this study with information on the possible extreme of such natural impacts.

Rare storm events not withstanding, the potential impacts confronting the marine ecosystem offshore of Sand Island and Honolulu Harbor are most probably those associated with chronic or progressive stresses. Because of the proximity of the population center and industry, marine communities fronting Honolulu Harbor are subjected to a wide array of impacts not usually occurring in other Hawaiian coral communities. Thus a sampling strategy must attempt to separate impacts due to wastewater treatment plant effluent on coral reef communities located at some distance shoreward from a host of other perturbations occurring in the waters fronting Honolulu.

Honolulu Harbor is the primary commercial port for the State of Hawaii and has been so since before the turn of the century (Scott 1968). The harbor is the result of dredging what was originally the drainage basin of Nu‘uanu Stream. This dredging commenced before 1900 and periodic maintenance dredging occurs up to the present time; up until about 1960 spoils were dropped just outside of the harbor generally to the east of the Honolulu Sewer Outfall. Besides shipping, the harbor is ringed with industry; pineapple canneries, gas and oil storage, and numerous other businesses are operating or have operated in the past. Storm drainage into the harbor and nearby Ke‘ehi Lagoon carries runoff from Honolulu’s streets and suburbs into the ocean. Pollution is well-known in the harbor and Cox and Gordon (1970) cite references describing these conditions as early as 1920. Sewage has been pumped into the ocean offshore of Kewalo and Sand Island since the 1930’s. These early inputs were all raw sewage released in water not exceeding 20 m deep. The actual point of release varied through time as different pipes were constructed and used. The multitude of perturbations that have occurred or are still occurring in shallow water (< 20 m) up until the construction of the present deep water outfall in 1978 may serve to obscure the impacts of the present discharge.

The waters fronting Sand Island into which the deep ocean outfall discharges may be considered in terms of gradients. There are numerous “gradients” due to point (storm drains, streams, etc.) and non-point inputs into Honolulu Harbor and environs from the above-mentioned activities. Because many of these inputs have been occurring for a considerable period of time, the species composition and functional relationships of the benthic and fish communities at any given location in the waters offshore of Honolulu are those that have evolved under the influence of these ongoing perturbations.

As noted above, if impacts are occurring in the shallow marine communities fronting Honolulu due to the deep ocean outfall, these are probably chronic in nature thus causing a slow decline in the communities so impacted. Gradients of “stress” or “impact” should be evident with distance from impact source(s). Thus to quantitatively define these impacts, one should monitor these communities through time in areas suspected of being impacted as well as in similar communities at varying distances away from the suspected source(s). This rationale has been used in developing the sampling strategy for this study.


The quantitative sampling of macrofauna of marine communities presents a number of problems; many of these are related to the scale on which one wishes to quantitatively enumerate organism abundance. Marine communities in the waters fronting Sand Island may be spatially defined in a range on the order of a few hundred square centimeters (such as the community residing in a Pocillopora meandrina coral head) to major biotopes covering many hectares. Because considerable interest focuses on visually dominant corals, diurnally exposed macroinvertebrates, and fishes, we designed a sampling program to attempt to delineate changes that may be occurring in communities at this scale.

Three sites were selected for the monitoring of benthic and fish community response to possible sewage impacts. The approximate locations of these sites (shown in Fig. 1) are close to some stations used by Dollar (1979). The sites and the rationale for their selection are given below:

Site A (Kewalo Landfill) was utilized as a control area lying east of the present deep ocean outfall in about 16 m of water (Fig. 1). Prevailing currents create a westerly movement of sewage effluent (Dollar 1979) thus the shallow Kewalo Landfill area is probably not directly impacted. At this location, corals occur in areas of emergent limestone. Local coverage over short linear distances may exceed 30 percent. This station is in the vicinity of Dollar’s (1979) Station 2.

Site B (Kalihi Channel) is located about 120 m east of the Kalihi Entrance channel in approximately 15 m of water. This station is about 900 m west of the bypass (old) outfall in an area heavily impacted by the old (1955–1977) shallow water discharge, and is very close to Dollar’s (1979) Station 14. Again there is emergent limestone at this station but coral coverage is low (< 1%).

Site C (Reef Runway) is located in an area of complex limestone substratum, in water ranging from 7.5 to 12 m deep fronting Honolulu International Airport’s Reef Runway. This station is close to Brock’s (1986) station that was monitored quarterly in 1977–78 (aecos, Inc. 1979) and again in 1986. It is close to Dollar’s (1979) Station 19. This site was moderately impacted by the old shallow water sewage outfall (Dollar 1979).

At each site two transect lines have been permanently established using metal stakes and plastic coated no. 14 copper wire. Transects are 20 m in length and have an orientation perpendicular to shore. Two transects have been established at each location to provide some replication. Both sample approximately the same benthic community. On each transect there are five permanently marked locations (0 m, 5 m, 10 m, 15 m, and 20 m) for taking photographs of the benthic communities. Cover estimates were also made in the field with a 1 ¥ 1 m quadrat placed at the -1 to 0 m, 4 to 5 m, 9 to 10 m, 14 to 15 m, and 19 to 20 m marks on the transect line in each survey.

Fish abundance and diversity is often related to small-scale topographical relief over short linear distances. A long transect may bisect a number of topographical features (e.g., coral mounds, sand flats, and algal beds) thus sampling more than one community and obscuring distinctive features of individual communities. To alleviate this problem, a short transect (20 m in length) has proven adequate for sampling many Hawaiian benthic communities (see Brock 1982, Brock and Norris 1989).

Information collected at each transect location includes a visual assessment of fishes, benthic quadrats for cover estimates of sessile forms (algae, corals, and colonial invertebrates) and counts along the transect line for diurnally exposed motile macroinvertebrates. Fish censuses are conducted over a 20 ¥ 4 m corridor (the permanent transect line) and all fishes within this area to the water’s surface are counted. A single diver equipped with scuba, and a slate and pencil enters the water, counts and notes all fishes in the prescribed area (method modified from Brock 1954). Besides counting the numbers of individuals of all fishes seen, the lengths of each is estimated; these length data are later used in the estimation of fish standing crop by linear regression techniques (Ricker 1975). Species specific regression coefficients have been developed over the last thirty years by the author and others at the University of Hawaii, Naval Undersea Center (see Evans 1974) and the Hawaii State Division of Aquatic Resources through capturing, weighing and measuring fishes; for many species the coefficients have been developed using sample sizes in excess of a hundred individuals. Two weeks were allowed to elapse from the time of station selection and marking to the time of the first fish census to reduce the bias caused by wary fishes. The same individual (R. Brock) performed all fish censuses to reduce bias.

Besides frightening wary fishes, other problems with the visual census technique include the underestimation of cryptic species such as moray eels (Family Muraenidae) and nocturnal species, e.g., squirrelfishes (Family Holocentridae), bigeyes or aweoweos (Family Priacanthidae), etc. This problem is compounded in areas of high relief and coral coverage that affords numerous shelter sites. Species lists and abundance estimates are more accurate for areas of low relief, although some fishes with cryptic habits or protective coloration (e.g., the nohus, Family Scorpaenidae; the flatfishes, Family Bothidae) might still be missed. Obviously the effectiveness of the visual census technique is reduced in turbid water and species of fishes which move quickly and/or are very numerous may be difficult to count. Additionally, bias related to the experience of the diver conducting counts should be considered in making comparisons between surveys. In spite of these drawbacks, the visual census technique probably provides the most accurate nondestructive assessment of diurnally active fishes presently available (Brock 1982).

A number of methods were utilized to quantitatively assess benthic communities at each station; these methods included the use of photographs taken at locations marked for repeated sampling through time (each covering 0.67 m2) and 1 ¥ 1 m quadrats also placed at marked locations for repeated measurements. The photographs and quadrats were both used to estimate coverage of corals and other sessile forms. Photographs provide a permanent record from which to estimate coverage and were used in 1991 and 1992; the 1 ¥ 1 m quadrats were used for an “in the field” appraisal of coverage in the three surveys. Cover estimates from photographs and quadrats were all recorded as percent cover. Diurnally exposed motile macroinvertebrates greater than 2 cm in some dimension were censused in the same 4 ¥ 20 m corridor used in the fish counts.

If macrothalloid algae were encountered in the 1 ¥ 1 m quadrats or photographs, they were quantitatively recorded as percent cover. Emphasis was placed on those species that were visually dominant and no attempt was made to quantitatively assess the multitude of microalgal species that constitute the “algal turf” so characteristic of many coral reef habitats.

As requested by permit agencies, simple physical measurements were made at the three sites while in the field. Measurements were made of percent oxygen concentration and temperature with a ysi Model 57 Oxygen meter, salinity was taken with a hand held refractometer and a 12-inch secchi disk was used to determine water clarity.

Data were subjected to simple non-parametric statistical procedures provided in the sas Institute statistical package (sas Institute 1985). Non-parametric methods were used to avoid meeting requirements of normal distribution and homogeneity of variance in the data. Data analysis utilized the Kruskal-Wallis one-way analysis of variance which was used to discern statistically significant differences among ranked means for each transect site and sample period; this procedure is outlined by Siegel (1956) and Sokal and Rohlf (1981). The a posteriori Student-Neuman-Keuls multiple range test (sas Institute, Inc. 1985) was also used to elucidate differences between locations.

During the course of the fieldwork, an effort was made to note any green sea turtles (a threatened species) within or near the study sites.


Field sampling was first undertaken on 27–29 December 1990. Station locations were selected and marked in November 1990 The permanent pins were deployed about a week later. Figure 1 presents the approximate locations of the three stations, each with a pair of transects; Figures 2, 3, and 4 are sketches showing the orientation of the permanent photographic quadrats on each transect line. The 1991 data were collected on 5–6 December 1991, and the 1992 information was taken on 21–22 December 1992 as well as on 25 January 1993 from the same locations.

Malfunction of a new Nikonos V camera caused the loss of all photographic quadrat data for all stations in the first (1990) field effort. Subsequently, the annual photography effort has been carried out by Mr. A. Muranaka (City and County of Honolulu). However, the 1990 visually assessed square meter quadrat data provided information on benthic coverage in this first annual effort. Subsequent surveys have used both photographic and quadrat methods to assess the benthic communities. It should be noted that the numbering of photoquadrats has changed from the 1991 and 1992 surveys but the locations are the same.

The results are presented below by station. All transects have an orientation that is perpendicular to shore.

Site A – Kewalo Landfill Station

This station is located 600 m offshore of the old Kewalo Landfill in water ranging from 17 to 18 m deep on a substratum dominated by limestone with moderate coral community development. The two transects are 35 m apart out of visual range of one another (see Fig. 2). Water clarity at this station is usually in the range from 15 to 20 m.

A summary of the data collected at Transect 1 in December 1992 is presented in Table 1. In the quadrat survey, six coral species were encountered having a mean estimated coverage of 18 percent; the dominant species are Porites lobata and Pocillopora meandrina. One algal species (Amansia glomerata) was noted in the quadrats. The macroinvertebrate census noted one cone shell (Conus lividus), two polychaetes (the Christmas tree worm - Spirobrachus giganteus corniculatus and the featherduster worm - Sabellastarte sanctijosephi), and three echinoderms (the long-spined sea urchin or wana - Echinothrix diadema, the sea star - Linckia diplax, and the boring sea urchin - Echinostrephus aciculatum). The results of the fish census carried out at Transect 1 are given in Appendix Table A. Table 2 presents the results of the photographic survey carried out on 3 August 1992. The mean coral coverage in the photographic survey was estimated to be 12.9 percent with Porites lobata being the dominant coral. Interestingly, in this survey an adult helmet shell (Cassius cornuta) was present in the 20 m quadrat occupying about 3 percent of the substratum.

In total 36 species of fishes and 312 individuals were encountered on Transect 1. The most common species include the yellowstripe goatfish or weke (Mulloides flavolineatus), the damselfishes (Chromis ovalis and C. vanderbilti) as well as the sleek unicornfish or kala holo (Naso hexacanthus). The standing crop of fishes on this transect was estimated to be 736 g/m2 and the species contributing most heavily to this biomass were the weke (Mulloides flavolineatus - 78% of the total biomass) and the kala holo (Naso hexacanthus - 7% of the total biomass).

Transect 2 was also established offshore of the Kewalo Landfill approximately 35 m west of Transect 1 in water ranging from 17 to 18.2 m deep. Table 3 presents a summary of the biological information collected at this transect site. The quadrat survey noted two macroalgal species (Amansia glomerata and Botryocladia scottsbergii) and six coral species (Porites lobata, P. compressa, Pocillopora meandrina, P. eydouxi, Leptastrea purpurea, and Montipora verrucosa) having an average coverage of 20.7 percent. The largest contributor to this coverage was Porites lobata. The estimated coral coverage has decreased approximately 8 percent since the 1991 survey, probably due to Hurricane Iniki which impacted the Hawaiian Islands on 11 September 1992. There were numerous broken coral fragments in the quadrats and elsewhere. The invertebrate census counted two polychaete species (the Christmas tree worm - Spirobranchus giganteus corniculatus and the featherduster worm - Sabellastarte sanctijopsephi), the pearl oyster (Pinctado marginifera), hermit crab (Aniculus strigatus), and one sea urchin species (Echinothrix diadema). The photographic quadrat survey carried out on 3 August 1992 (before the hurricane) noted three algal species (mean coverage 2%), an unidentified red sponge, and four coral species with a mean coverage of 27.8 percent (Table 2).

The results of the fish census are presented in Appendix Table A. Twenty-six fish species were identified (240 individuals) on this transect; the most abundant species included the yellowstripe goatfish or weke (Mulloides flavolineatus) and the damselfish (Chromis vanderbilti). The standing crop of fishes was estimated to be 247 g/m2. The species that contributed the most to this estimated weight was the yellowstripe goatfish or weke (Mulloides flavolineatus - 93% of the total biomass).

Site B – Kalihi Entrance Channel

Two transects (numbers 3 and 4) were established on a limestone substratum about 120 m east of the Kalihi Entrance Channel in 13.7 to 15 m of water. This station is located about 2.2 km seaward of Mokauea Island situated in Ke‘ehi Lagoon, and about 900 m west of the old outfall which is now used as an emergency bypass. Much of the substratum in the vicinity of this station is comprised of sand and rubble. An area of low emergent limestone approximately 60 m wide and 110 m in length with the long axis oriented perpendicular to shore is present. Transect 3 is located on the deeper end of this hard substratum area. Transect 4 parallels Transect 3 but is shoreward of this and approximately 8 m to the west (see Fig. 3). During the 1992 survey water clarity at this station ranged from 10 to 27 m during our visits. The lack of appropriate hard substratum necessitated establishing the two transects at this station on an “end to end” fashion relatively close to one another (8 m apart). Because of the close proximity, the fish censuses at these stations were carried out on both transects prior to any other data collection.

Transect 3 has an orientation perpendicular to shore on the limestone substratum in water 14.6 to 15 m deep. Table 4 presents a summary of the biological observations made at Transect 3. The quadrat survey noted two algal species (Desmia hornemannii and limu kohu or Asparagopsis taxiformis together having a mean coverage of 0.1%), the red encrusting sponge (Spirastrella coccinea), one soft coral (Palythoa tuberculosa), and four coral species (Porites lobata, Pocillopora meandrina, Montipora verrucosa, and M. patula) having a mean estimated coverage of 2 percent (a decrease of 2% over previous surveys). The invertebrate census noted one rock oyster (Spondylus tenebrosus), octopus or he‘e (Octopus cyanea), and three sea urchin species (Echinostrephus aciculatum, Echinometra mathaei and Echinothrix diadema) as well as the starfish (Linckia diplax). The photographic quadrat survey found an unidentified red sponge species and four coral species (Porites lobata, Pocillopora meandrina, Montipora verrucosa?, and Fungia scutaria) having a mean coverage of 4 percent.

The fish census (App. Table A) found 15 species, 33 individuals and an estimated standing crop of 30 g/m2. The most abundant fishes at Transect 3 included the manybar goatfish or moano (Parupeneus multifasciatus) and the lei triggerfish or humuhumu lei (Sufflamen bursa). The fish species contributing heavily to the biomass on Transect 3 included a single tableboss or a‘awa (Bodianus bilunulatus making up 38% of the biomass), an orangebar surgeonfish or na‘ena‘e (Acanthurus olivaceus - 19% of the total), a rockmover (Novaculichthys taeniourus - 14%), and five humuhumu lei (Sufflamen bursa - 14% of the total weight).

Transect 4 also sampled the benthic and fish community present in the vicinity of the Kalihi Entrance Channel. As with the previous transect, Transect 4 sampled the limestone substratum at a depth ranging from 13.7 to 14 m. Table 5 presents a summary of the biological data collected on Transect 4. The quadrat survey noted two algal species (Desmia hornemannii and limu kohu or Asparagopsis taxiformis), the red sponge (Spirastrella coccinea), and four coral species (Porites lobata, Pocillopora meandrina, Montipora verrucosa, and M. patula). Coral coverage was estimated to be 3.2 percent and both Porites lobata as well as Pocillopora meandrina were the major contributors to this coverage. The invertebrate census noted one small cone shell (Conus lividus), four sea urchin species (the boring urchin - Echinostrephus aciculatum, the green urchin Echinometra mathaei, and long spined urchin or wana - Echinothrix diadema) as well as the starfish Linckia diplax. In the photographic quadrat survey an unidentified red sponge species was seen and two corals (Porites lobata and Pocillopora meandrina) having a mean coverage of 6.3 percent.

The fish census noted 27 individual fishes among 9 species (App. Table A). The most common fishes present on this transect include the twospot wrasse (Cheilinus bimaculatus) and the lei triggerfish or humuhumu lei (Sufflamen bursa). The standing crop of fishes on Transect 4 is estimated to be 14 g/m2 and the important contributors to this biomass include a stripebelly puffer or keke (Arthron hispidus - 46% of the total) and the lei triggerfish or humuhumu lei (Sufflamen bursa) which contributed 30 percent of the total weight present at this transect site.

  1   2   3

Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur © 2016
rəhbərliyinə müraciət